Lead-acid storage batteries comprise several cell elements each encased in separate compartments of a container containing sulfuric acid electrolyte. Each cell element comprises at least one positive electrode, at least one negative electrode, and a porous separator (i.e. a thin microporous sheet and/or absorbent glass mat) therebetween. The electrodes each comprise a reticulated lead (including lead alloys) substrate, called a grid, which supports an electrochemically active material thereon, and conducts electrical current throughout the electrode. The active material comprises a leady material (i.e. PbO, PbO.sub.2, Pb, or PbSO.sub.4 at different charge/discharge stages of the battery) pasted onto the grid.
Many lead-acid batteries are so-called "maintenance-free" batteries which are characterized by having low self discharge, and not requiring the addition of water or other maintenance throughout their lives. Typically, such batteries include grids which are made from lead-calcium alloys that may also contain other alloyants such as tin, strontium, barium, inter alia (see for example Prengaman U.S. Pat. No. 3,953,244 , Nees et al. U.S. Pat. No. 4,137,378 and Matter U.S. Pat. No. 4,228,580). As used herein the term lead-calcium alloy is not intended to be limited strictly to such metals, but rather to include other metals and elements as well which are not deleterious to the battery or the maintenance-free character thereof, and are well known to those skilled in the art. The lead-calcium grid alloy may be cast directly into grids, cast into ribbons which are subsequently expanded into grids, or rolled into ribbons in a rolling mill to form wrought alloy ribbons which are subsequently expanded into grids. In one expansion process, a grid-forming ribbon is expanded, in guillotine fashion, by successively advancing the ribbon between slitting and stretching dies such that short interconnected skeletal segments are peeled away from the leading edge of the ribbon to form a tiered structure of polygonal paste retaining cells. Another expansion technique is the dual expansion guillotine type process for making battery grids from Pb-alloy ribbons as disclosed in Daniels et al. U.S. Pat. No. 3,853,626 , which is assigned to the assignee of the present invention and incorporated herein by reference.
SLI lead-acid batteries having positive electrodes made from lead-calcium alloy grids are relatively short-lived as determined by the SAE J240B Life Cycle Test (at 40.degree. C. and particularly at 75.degree. C.) owing to corrosion of the grid surface which forms an electrically resistive layer between the active material and the grid and seemingly reduces the adhesion between the active material and the grid over the course of the test. Lead-calcium grid batteries are particularly susceptible to early failure of the high temperature (i.e. 75.degree. C.) J240 test. Deep cycling Pb-Ca grid batteries suffer from the same malady, and are similarly short-lived compared to similar batteries made with Pb-Sb grids.